High performance mortars from vitrified bauxite residue; the quest for the optimal chemistry and processing conditions

This study investigates the transformation of bauxite residue into a reactive precursor after heat treatment at 1200–1300 °C and the synthesis of high performance inorganic polymer mortars thereof. Minor amounts of C, CaO and SiO2 were added to bauxite residue, and the melt was water-quenched resulting in amorphous phase (25 up to 62 wt%), the rest being mainly iron-rich phases. After milling the vitrified bauxite residue, alkali-activated mortars were produced with a maximum compressive strength of 131 MPa after 28 days at ambient curing. Calcium was identified as key element in increasing the compressive strength, reduction in shrinkage and permeability. The release of heavy metals and radionuclide concentration were below legislative limits. This work identified an ideal chemistry for producing high-performance binders from precursors containing more than 81 wt% of bauxite residue, opening the possibility of upscaling and, eventually, the real-life transformation of bauxite residue into a product.